Extrusion cut-off

ABSTRACT

AN EXTRUSION FOLLOWER BLOCK TO BE POSITIONED BEHIND A BILLET IS PROVIDED WITH AN OUTER PORTION OF MATERIAL MORE READILY DEFORMED THAN THE BILLET AND INNER MEMBERS LESS READILY DEFORMABLE THAN THE BILLET.

United States Patent [72] Inventor Paul Loewenstein LineolmMas. 211 Appl. No. 749,055 22 Filed July 31,1968 [45] Patented June, 1971 [73] Assigne'e Whittaker Corporation, Nuclear Metal Division, Concord, Mass.

[54] EXTRUSION CUT-OFF 6 Claitu,5 Dnwhg Figs. [52] 11.8. 72/273, 29/1875 [51] Int. Cl B210 25/00 [50] Field olSeu-eh 72/273,42; 29/187.5, 195:207/183, 10.21

[56] References Cited UNITED STATES PATENTS 1,125,162 6/1911 Page 29/187.5X

Primary Examiner- Richard J. Herbst Assistant Examiner-A. L. Havis Attorneys-Donald E. Nist and Jay H. Quartz ABSTRACT: An extrusion follower block to be positioned behind billet is provided with an outer portion of material more readily deformed than the billet and inner members less readily deformable than the billet. l

' EXTRUSION CUT-OFF This invention relates to the extrusion of metals, and more particularly to extrusion cutoffs or follower blocks.

The extrusion of metals is usually carried out in a hydraulic press-type device comprising an extrusion chamber or containing area into which is placed a metal billet to be extruded. A die is suitably affixed to one end of said extrusion chamber, and the other end of the chamber is suitably adapted to receive a force means or ram which enters the container and presses against the end of the metal billet opposite that presented before the die, transmitting to said billet the force developed by the press, so as to force the metal billet through the die.

In the past, certain members commonly called dummy blocks, were placed between the force means or ram, and the end of the extrusion billet. While there are a number of advantages to the use of a dummy block, in general, they were employed for one of two basic reasons: either to protect the extrusion die from damage by the ram, or to transmit the force from the ram to the extrusion billet in a particular manner. In general, these so-called dummy blocks were of such a nature, or of such a design, as would be permanently damaged if any part of the dummy block were forced through the extrusion die; or at the very least, in such an occurence, major repair work would be required to restore the dummy block to a useful configuration.

Several major problems have been encountered in the extrusion of metals by existing means whether a dummy block was used or whether the ram was directly transmitting the force to the extrusion billet. One problem was the difficulty in pushing all of the metal extrusion billet through the extrusion die, especially where the metal being extruded was a precious metal or a rare metal of very high cost. A second major problem was the removal of the so-called discard which remains attached to the extrusion die; the discard having at one of its ends a diameter essentially equal to the original diameter of the extrusion billet, while at its other extremity it has a diameter which has been reduced to that of the die orifice in the extrusion die. It has been found that in almost every case, it is extremely difficult to remove the discard from the extrusion die, an operation made desirable by the extremely high cost of extrusion dies, particularly extrusion dies having a shaped orifice; that is to say, an orifice designed to produce an extruded rod of a structural shape.

It is, therefore, one object of the present invention to provide an extrusion cutoff or follower block which will insure complete extrusion of the metal billet.

It is another object of this invention to provide an extrusion cutoff or follower block which can be partially extruded to force all of the metal billet through the extrusion die and yet can be easily removed from the extrusion die.

It is a yet further object of this invention to provide an extrusion cutoff or follower block which may be partially extruded in order to force all of the metal billet through the extrusion die wherein the extruded part of said follower block may be quickly and inexpensively placed in a condition for reuse.

Other objects, features and advantages of the present invention will in part be obvious and will in part be seen from the following detailed description taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a cross-sectional view of one follower block of the present invention.

FIG. 2 is an alternative embodiment of the extrusion cutoff or follower block of FIG. 1.

FIG. 3 is a diagrammatic illustration of an extrusion assembly, before extrusion, using the extrusion cutoff of the present invention.

FIG. 4 is a diagrammatic illustration of the extrusion assembly of FIG. 3 shown during extrusion.

FIG. 5 is a diagrammatic illustration of the extrusion assembly of FIG. 3 shown after extrusion has been completed.

The novel extrusion cutoff or follower block of the present invention comprises a member which essentially conforms to and is adapted to fit within the extrusion chamber of a ramtype extruder, said member comprising a graphite outer portion surrounding and reinforced by one or more reinforcing members. In the preferred embodiment of the present invention, the surface or surfaces of the follower block which are adjacent to or in contact with the wall of the extrusion chamber are of graphite, and the graphite is reinforced by one or more steel reinforcing members which may be tubes, rods, bars, or in fact, any shape which will conveniently fit within a predisposed area or areas of the graphite outer member.

The follower block of the present invention is used by placing it in an extrusion chamber, between the ram and the billet. As the extrusion is carried out, the entire billet will be extruded and a portion of the follower block will also be extruded. As the extruded portion of the follower block passes through the extrusion die, the entire cross section is reduced. proportionately by streamlined flow and only the metal comes out as a solid rod because the graphite is broken down into a powder and falls away from the metal reinforcing members. When the extrusion is stopped, the extrusion die can be easily disengaged from the follower block by a very slight push or pull because the only material in intimate contact with the extrusion die is graphite powder.

The present invention takes advantage of a number of principles or concepts well known in metal extrusion technology including:

1. Streamlined Flow, which is the term used in extrusion technology to describe the effect obtained when a cylindrical billet is forced through a round die with a nearly conical opening. In this situation, any point in or on the billet, maintains its same relative position in the extruded rod, and, therefore, the cross section of the billet will be faithfully reproduced with reduced area in the extruded rod. The process is somewhat analogous to photographic reduction.

2. Extrusion Resistance is a very important constant which is universally relied upon by those skilled in the extrusion art. Every material which can be extruded has a relative stiffness, or resistance to extrusion, hereinafter designated K. This is a constant at any given temperature and it usually decreases with increasing temperatures. The constant for most materials over a wide temperature range is well known to those skilled in the art of extrusion technology.

3. Relative Stiffness, is the resistance to deformation in extrusion and is defined by the equation,

=P/In R where K is the relative stiffness or extrusion constant mentioned above, P is the pressure for extrusion, and R is the reduction in area (or the cross-sectional area of the billet divided by the cross-sectional area of the extruded rod). As previously noted, most materials have an extrusion constant at a specific temperature, and this constant for any given material, at any given temperature is well known to the extrusion technologist.

4. Coextrusion is the simultaneous, streamlined extrusion of different materials, often two different metals, which have similar extrusion constants.

5. Composite Stiffness is a property of a coextrusion billet which contains materials of different extrusion constants. The property is generally used in extruding an extremely stiff material by coextrusion with a softer material. Often, to extrude a material at a chosen temperature and reduction in area, the force required to extrude is in excess of the press capacity, or more commonly in excess of the stress limitations of the extrusion tools, usually about I00 tsi or less. This limitation can be overcome by canning or encasing the stiff material in a softer material and coextruding it under streamlined conditions. However, the softer material must not be too soft or streamlined flow will not occur. In these cases, the composite billet extrudes at a force related to its composite stiffness, which is in turn related to the fractional area and stiffness of each component in the billet. An example is the coextrusion of tungsten ina steel canning or enclosure because the tungsten is much stiffer than the steel.

On the other hand, it is sometimes desirable to extrude a soft material at a higher pressure. In this case, it is frequently possible to coextrude the softer material in a canning or enclosure of stiffer material. An example is the coextrusion of aluminum in a copper can because the former is much softer than the latter. Here again, the billet extrudes with a force related to its composite" extrusion stiffness or constant.

Those skilled in the art of metallurgy have long sought a follower block which could be used both in the extrusion, of expensive metals and/or alloys, where complete extrusion of the metal is economically most desirable; and/or which could be used in extrusions of metals through a so-called shaped extrusion die. A shaped extrusion die is one which will produce an extruded rod of a so-called structural shape; that is, a rod having a cross sectional configuration in the shape of T, a U, or other well-known shapes; such dies being extremely expensive, quite intricate, and most difficult to separate from the socalled discard.

The use of graphitein the follower block was considered impossible because pure graphite used as the follower block in the extrusion of metals would not have sufficient extrusion resistance at the pressures employed. As soon as a pure graphite follower block reached the extrusion die, it would immediately rush through the die orifice almost as a liquid, allowing the ram to jump forward, causing severe if not irreparable damage to the extrusion die, the extrusion chamber and/or the ram itself. Even more serious than the damage to the equipment, the extruded billet itself would be pushed through at a greatly increased velocity distorting the extruded product and causing a serious safety hazard.

The novel follower block of the present invention overcomes the prior drawbacks of graphite by inserting metal reinforcing rods in the graphite. This essentially creates a separate coextrusion billet, which, as noted above, has a composite stiffness.

In certain instances, metals, including steel, have been used as a type of follower block to push all of an extremely expensive billet through the extrusion die, but it has been, until now, almost impossible to remove the steel block from the extrusion die; that is to say, they could not be disengaged. This same limitation applied to the known dummy blocks mentioned above. Metal follower blocks could only be employed where the extra metal to be salvaged was of a sufficiently high value to compensate for the almost certain loss of the extrusion die.

The follower blocks of the present invention are clearly distinguishable from the dummy blocks used in earlier metal extrusions. The dummy block is, in general, undeformable while the follower block is defonned in the same manner as the billet. Also, the dummy blocks as noted above were almost always of a special, and often times, complex structure specifically designed either to present the rearward end of the extrusion billet to the extrusion die at a particular predetermined position and/or to transmit the force from the ram to the billet in a very special or particular manner. For example, mention might be made of the spherical dummy block disclosed in claim in the U.S.'Pat. No. 3,l8l,335 to R. D. Webber where the spherical dummy block member having a diameter slightly smaller than the diameter of the cylindrically-shaped extrusion chamber was placed between the ram and the extrusion billet so that the forces were transmitted through the dummy member to the billet in such a way that the maximum force was applied along the axis of the billet, and a minimum of force was applied at the periphery, while at the same time the cylindrically-shaped dummy block would tend to fill most of the open area in the tapered end of the extrusion chamber adjacent to the extrusion die, so that a maximum amount of the billet would be pushed through the extrusion die. It should be noted, however, that not all of the billet would be pushed through unless the dummy block member itself were partially extruded, and if the cylindrically-shaped dummy block member were partially extruded, it would be completely destroyed, or, could only be reused after being completely melted down and reshaped back to its original size and configuration by long and expensive metallurgical steps and recovering procedures.

As shown in FIG. 1, the normal follower block comprises a cylindrical mass of graphite 1 having a plurality of cylindrically-shaped openings 2a--2f running parallel with its transverse axis, and a plurality of cylindrically-shaped metal reinforcing members, Zia-31 disposed within said openings.

An alternative embodiment of the present invention is illustrated by FIG. 2 and comprises an outer tube of graphite 11 and a plurality of alternate concentric shells of graphite l2 and steel 13 surrounding a central graphite core 14.

It will, of course, be recognized that the general configuration of the follower block in FIG. 1 and in FIG. 2 is an essentially cylindrically-shaped member, but could as easily be elliptical, square, or rectangular, in its cross-sectional configuration, depending upon the cross-sectional configuration of the extrusion chamber in which it is to be employed.

The follower block of the present invention would find equal application in the extrusion of tubes where the billet is disposed on an undeformable mandrel which determines the inside diameter of the tube. Where a mandrel is to be employed in the extrusion, a follower block of the present invention could be a cylinder of graphite having a hole in its center to accommodate the mandrel, and having metal reinforcing rods disposed within some portion of the remaining area, in such a manner that only graphite would be in contact with the walls of the extruder or the outer surface of the mandrel. The preferred embodiment of the present invention, for use in extrusions employing a mandrel would be a follower block composed of a series of concentric tubes of graphite and metal, the smallest being a graphite tube having an inside diameter slightly larger than the diameter of the mandrel, and the largest tube being a graphite tube with an outside diameter slightly smaller than the inside diameter of the extrusion chamber.

As has been noted above, the follower block of the present invention can be economically constructed and placed between the extrusion billet and the ram and partially extruded so as to force all of the extrusion billet through the extrusion die. FIGS. 3, 4, and 5 are diagrammatical illustrations of an extrusion using the follower block of the present invention; the metal billet 2] is contained within an extrusion chamber defined by wall members 22. An extrusion die 23 is suitably attached to one end of the extrusion chamber and a ram member 24 is suitably disposed at the other end of the extrusion chamber, said ram being suitably connected to a means whereby it can be forced in a direction through the extrusion chamber towards the extrusion die, and a follower block member 25 is disposed between the said billet 21 and said ram 24.

As shown in FIG. 4, the same elements are now shown at a point mid way through the extrusion and an extruded rod 26 as now shown has come through the extrusion die, extruded rod 26 being the extruded billet 21. FIG. 5 depicts these same elements at a still later stage of the extrusion and shows a completely extruded rod 26, an extruded portion 27 which is the extruded portion of the follower block; the remainder of the follower block is still within the extrusion chamber and the ram is quite well within the extrusion chamber forcing the follower block through the extrusion die.

It will, of course, be obvious to those skilled in the art, that where extremely high extrusion pressures will be required, a still further alternative embodiment of the follower block of FIG. 1 might be employed. While not shown in the FIGS., such a block would consist of a relatively thin wall tube of graphite and a single large mass of steel having a diameter slightly less than that of the inside diameter of the graphite tube, said steel rod being disposed within said graphite tube.

It is possible within the scope of the present invention to use a wide variety of materials in the construction of the novel follower block. For example, almost any metal can be used; but one must keep in mind that the primary purpose of using the follower block is to save money; which means that many otherwise suitable materials would be far too expensive. The graphite could also be replaced by other powdered materials having similar extrusion resistance, e.g., common salt (NaCl It is well known in the art of extrusion, as previously noted, particularly in the art of metal extrusion, that where more than one material is being concurrently extruded through a conical die which would produce streamlined flow in the extrusion billet, e.g., proportional reduction of each component of the billet, the resistance to extrusion of the various components, and

the composite billet, or in this case the composite follower block, has a single resistance to extrusion, and will, when forced through a conical die as described above, yield essentially a photographic type reduction, completely proportional between each of the members. It is important to keep this in mind, since one might otherwise think that the graphite will be forced through the die and will then be followed by an extrusion of the steel which will then still become permanently, or at least semipermanently engaged with the extrusion die; in fact, as noted above, it is well known that this will not happen and that a completely proportional reduction will be obtained. For example, if we were to take a graphite tube having a oneinch outer diameter, and a one-half inch inner diameter, and place within it a steel rod of the same length having a diameter of 0.48 inches, and if we were to pass this through a conical extrusion die having a die orifice of one-quarter inch, the extruded rod coming from the die would consist of a one-quarter inch rod with a one-sixteenth inch wall of graphite surrounding a one-eighth inch steel center (the graphite would, of course, fall away as powder).

It will, of course, be obvious to those skilled in the art, that many changes can be made in the above invention without departing from the nature or scope thereof, and it is my intention to be limited only by the appended claims.

lclaim:

1. An extrusion follower block for positioning behind a billet to be extruded and consisting essentially of an outer member of a material more readily deformable than that of the billet to be extruded and which corresponds to the configuration of, and is attached to fit within, an extrusion chamber, and at least one continuous member disposed within said outer member and of a material less readily deformable than the outer member, the composite stiffness of the follower block being intermediate that of the outer member and the billet to be extruded.

2. An extrusion follower block comprising a tube of graphite having a wall thickness less than 20 percent of its outside diameter, a plurality of steel reinforcing members disposed within said graphite tube, a plurality of graphite rods disposed within said tube, said graphite rods and said metallic rods being randomly disposed within said tube and each of said rods being disposed with its axis parallel to the axis of the graphite tube.

3. An extrusion follower block according to claim 1 in which said at least one inner member comprises a plurality of rods disposed within the outer member, separated from each other by the material of the outer member, and having longitudinal axes disposed parallel to the longitudinal axis of the outer member.

4. An extrusion follower block according to claim 1 in which said outer member comprises a generally cylindrical graphite body and in which said inner members comprise steel rods disposed within said outer member.

5. An extrusion follower block according to claim 1 in which said at least one inner member comprises a first set of concentric shells separated from each other by a second set 0 concentric shells which form said outer member.

6. An extrusion follower block according to claim 5 in which said second set of shells includes at least one graphite shell forming the outer shell of said outer member.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 7,282 Dated une 28, 1971 Pa Inventor(s) ul teln It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

The sheet of drawing and the drawing on the front page format should be canceled and the attached drawings'and drawing figure substituted therefor:

Signed and sealed this 13th day of March 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PO-IOSO (10-69) USCOMM DC 0031b? 1 04s. GOVERNMENT rnnmuc arm: nu macs-3:1.

PATENIEnJuummn 3 587-282 sum 1 or 2 INVENTOR PAUL LOEWENSTEIN 

